The process of this invention is an improvement in the process disclosed and claimed in U.S. Pat. No. 3,566,067 issued Feb. 23, 1971 to Daniel A. Larson for "Method Of Sealing Off Refractory Metal Tubulation By Tube-In-Circuit Electric Heating".
U.S. Pat. No. 3,566,067 discloses a process which involves a two-step compressing operation wherein the tubulation is first flattened with a pair of flattening jaws followed by a second press employing curved jaws which reduces the thickness of the press to approximately the wall thickness of the tubulation and thereby provide a high resistance section for the subsequent passing of electric current through the tubulation to cause the tubulation to separate at the center of the press and provide a seal at the end thereof. Although this method of sealing off the refractory metal exhaust tubulation of a ceramic arc tube employed in a high pressure discharge lamp has proved reasonably successful, in some instances because of the very thin section of tubulation at the point of separation and the current levels necessary to cause the melting and separation, some of the metal in this thin area is flashed away resulting, in some instances, in unreliable seals.
In addition to the foregoing deficiency of the prior art process, reduction of processing steps is a further goal in the high speed manufacturing of all types of lamps. Elimination of one of the pressing steps would therefore be a further desirable improvement. Additionally, the process as previously practiced required the entire arc tube to be disposed in an inert gas atmosphere during the processing of the arc tube and as such, is a piece work operation which cannot be performed on automated indexing equipment.